The roof of cavern is regarded as an elastic beam with support at the midpoint and the coal pillars are regarded as bearings so as to establishing a cavern roof-coal pillar system.The influence of strain gradient is taken into account in the constitutive relation of coal or rock,the instability criterion of coal pillar is given,the influence factors of rock burst in coal pillar are analyzed.It is indicated that the span and flexural stiffness of cavern roof,the dimension and brittleness of coal pillar,the uniformity of coal material and the size of mineral grain are the important factors influencing rock burst of coal pillar.